This research project is directed toward the further development (with evaluation of rehabilitative benefits in profoundly deaf human subjects) of an intracochlear multichannel electrical stimulation prosthesis. Physiological and histopathological studies shall provide further crucial information about potentially applicable multielectrode stimulating arrays, and about safety of their long term stimulation. They shall also provide additional techniques for evaluating the multielectrode array performance in implanted patients; and studies required before implantation of these prosthetic devices in children can be considered shall be initiated. These devices shall be implanted in a small number of postlingually deaf patients in whom deafness is profound, and in which there is a high probability of good acoustic nerve survival. These multichannel prostheses encode speech sounds and deliver coded stimuli to a series of discretely stimulated sectors of the auditory nerve array. The implant device can be interfaced with a computer system capable of processing speech signals into different stimulus formats that can be delivered to the electrode array. This system will be used to determine the perceptual consequences of employing different speech processing formats. This information is required for development of optimum stimulus processors-transmitters for patient use. Patients will undergo comprehensive pre- and post-operative audiological evaluation. Quantitative comparisons will be made in the improvement in communicative skills in different groups of profoundly deaf patients provided with carefully fitted hearing aids and multichannel intracochlear prosthetic devices. Patients receiving hearing aids and intracochlear electrical stimulation multichannel prostheses will participate in an intensive aural rehabilitation program. These patient studies should provide an objective definition of the relative benefits and potential wider application of optimally designed cochlear implants for the larger population of the profoundly deaf.